1. Field of the Invention
This invention lies in the field of cathode ray tube technology. More particularly, it involves a method of adjustment of the flyback transformer in the cathode ray tube control system, to provide optimum tuning of the transformer, such that there will be a minimum of ringing or oscillatory signal in the voltage wave-form in the high voltage coil.
2. Description of the Prior Art
It is well known that the flyback transformers in video devices such as TVs, display terminals, etc. can be tuned to provide maximum efficiency, and high voltage, as well as to avoid a curtain effect in the raster, due to oscillations or ringing in the voltage generated.
The degree of tuning is easily observed by viewing the high voltage wave-form on a cathode ray oscilloscope. Optimum tuning is obtained by minimizing the amplitude of ringing, which appears on the base line of the wave-form. When the ringing frequency is the third harmonic of the frequency of the principal peak of the high voltage wave-form, optimum tuning is realized.
This tuning has been accomplished in a variety of ways in the prior art. One popular method involves controlling the size and shape of the high voltage coil. This approach controls high voltage coil leakage inductance and capacitance. Tuning can also be accomplished by changing the dimension of the air gap in the core, to control the fundamental flyback frequency.
Although both of these methods are fairly effective in flyback tuning, they are both cumbersome, and each has certain limits. For example, in the control by varying the dimensions of the high voltage coil, these parameters must be optimized by a procedure of successive approximations. Once the dimensions are chosen, they must be held closely in production, or coils will not be useable.
So far as gap changes in the core are concerned, this procedure can be performed by removing the flyback core and testing various thicknesses of the gap material between the core halves. However, the primary inductance must be optimized specifically for tuning. Since it cannot be optimized for minimum transformer current and best core flux density, maximum circuit efficiency cannot be realized.